Ok, ok. Let me give you guys some example of changes a.k.a Stimuli
Stimuli is known to us as touch, pain, heat, cold, sounds, food (chemicals) and light.

Let me further explain the stimuli to you.
- You feel and touch objects, that is a stimuli
- You look at things around you, that is a stimuli
- You feel cold, or hot, that is a stimuli
- You feel pain whe you fall down, that is a stimuli
- You hear sound, that is a stimuli
- You taste a burger, that is a stimuli

By now you should know what is astimuli. But, in our daily life, we deal with millions of stimuli and we call that Stimulus, which mean a lot of stimuli or plural form of stimuli.

When a stimuli or stimulus come to us. We response to it or them.
For every stimuli there is a response to it weather we aware or not. For example, when we touch anything hot like iron, we will feel pain. The response would be pulling back the hand to avoid pain.

Human need to respond to stimuli in order to protect themselves from danger or for survival.